Pulmonary ischaemia without pulmonary arterial thrombus in COVID-19 patients receiving extracorporeal membrane oxygenation: a cohort study.

AIM: To evaluate the incidence of pulmonary ischaemia in COVID-19 patients on extracorporeal membrane oxygenation (ECMO), and its correlation with pulmonary artery thrombosis. MATERIALS AND METHODS: Computed tomography (CT) thorax of all patients receiving ECMO with proven COVID-19 pneumonitis between March and May 2020 were analysed for the presence and extension of pulmonary thromboembolic disease. RESULTS: Fifty-one patients were reviewed. The mean (range) age of 45 (26-66) years; 38/51 (74.5%) were men. All patients had severe COVID-19 pneumonitis, and 18/51 (35.3%) had macroscopic thrombosis (15 with associated ischaemia); however, 13/51 (25.5%) patients had ischaemia without associated thrombus. CONCLUSION: The majority of patients with COVID-19 who received ECMO had areas of ischaemia within consolidated lungs, almost half of these without subtending pulmonary artery thrombosis. Although the prognostic significance of these findings is unclear, they are highly suggestive of lung ischaemia due to isolated microvascular immune thrombosis.

Psoas muscle atrophy following unilateral hip arthroplasty.

BACKGROUND: Studies have demonstrated the presence of muscle atrophy around the hip in patients with hip osteoarthritis. Few studies have examined the psoas muscle or assessed it at a paraspinal level in patients post-total hip arthroplasty. The aim of this study was to determine if there is significant psoas muscle atrophy as indicated by muscle cross-sectional area and high degree of fat infiltration post-unilateral hip arthroplasty. METHODS: Retrospective analysis of 341 patients with unilateral hip implant and subsequent lumbar spine MRI over a 8-year period was performed. Fat infiltration and cross-sectional area of the psoas muscle at L3/4 level were measured by two musculoskeletal fellows (1 year experience in musculoskeletal radiology), and comparison made between the implant and non-operative sides was made. Fat infiltration was measured using the modified Goutallier grading. The degree of hip osteoarthritis in the non-operative side was measured using the Kellgren-Lawrence grading. The data was analysed using paired t test, ANOVA, unpaired t test, Pearson correlation and Jonckheere-Terpstra test. RESULTS: The cross-sectional area of the psoas muscle on the implant side was significantly less than the non-operative side. There was significance between the cross-sectional area difference and the fat grade of the implant side. CONCLUSION: Our results demonstrate psoas atrophy on the implant side compared to the non-operative side in post-unilateral implant patients. Post-operative hip implant rehabilitation may benefit from more focused psoas strengthening exercises to improve functional outcome.

Ex vivo interaction between blood components and hormone-dependent breast cancer cells induces alterations associated with epithelial-mesenchymal transition and thrombosis.

The prevalence of breast cancer is steadily increasing with metastasis and thromboembolic complications identified as the most common causes of death. The acquisition of an aggressive phenotype by hormone-dependent breast cancers is mediated by Transforming Growth Factor Beta 1 (TGF-ß1) expression and is associated with epithelial-mesenchymal transition (EMT) and, potentially, increased propensity for thrombosis. We investigated this phenomenon by assessing the effect of platelet-rich plasma (PRP) and whole blood (WB) on parameters of EMT and hypercoagulation in vitro. MCF-7 breast cancer cells were cultured under standard conditions, followed by co-culture with PRP or WB. Cells were processed for real-time PCR (TGF-ß1 and vimentin), electron microscopy or immunocytochemistry (TGF-ß1). Micrographs were qualitatively assessed, and real-time PCR data analyzed with PAST Statistical Software. The addition of blood components heightened TGF-ß1 immunolocalization and significantly increased corresponding gene expression. Both PRP and WB significantly increased vimentin expression and induced a shape change from a typical epithelial phenotype to a spindle-shape morphology, indicative of EMT. Fibrin fiber, network and plaque formation indicated a hypercoagulatory environment. The results thus show that in preparation for hematogenous metastasis, hormone-dependent breast cancer cells assume an aggressive phenotype associated with EMT, simultaneously increasing the propensity for the formation of thrombo-emboli.

Awareness of fertility preservation among Chinese medical students.

INTRODUCTION: The fertility preservation (FP) services offered in Hong Kong are underutilised. There have been no previous studies on Chinese medical students to investigate the underlying reasons for this underutilisation in terms of awareness, knowledge, and attitudes towards FP and age-related fertility. METHODS: This was a cross-sectional survey among Chinese medical students in Hong Kong. RESULTS: The majority of participants (77.8%) were not familiar with any clinics or specialists who provide FP services. The vast majority (88.1%) underestimated female infertility at age 45 years, and 89.8% overestimated the age of male fertility decline. The students' FP knowledge was mainly acquired from electronic media (58.4%) and medical school (57.6%). Medical students showed overwhelming support towards FP for medical reasons (97.9%) but had mixed responses about FP for elective reasons related to career development in women (58.8%). Of the participants, 80.2% agreed that the government should subsidise FP services for patients with medical reasons. CONCLUSION: This study highlights the limited awareness and knowledge of FP among Chinese medical students. There is a strong worldwide need to increase education about and exposure to FP in the medical curriculum and improve medical students' knowledge.

A fuzzy probabilistic method for medical diagnosis.

The max-min composition in fuzzy set theory has attained reasonable success in medical diagnosis in the past thirty years for estimating the probability of a patient diagnosed with a certain disease. However, there has been no theoretical justification why the method would work. We create a theoretical model to calculate the probabilities of hypothetical patients having designated diseases, and use simulated dataset to explain why the max-min composition has been successful. In addition, based on the theoretical model, we propose a fuzzy probabilistic method to estimate the probability of a patient having a certain disease. The proposed method may produce a more accurate estimate than the max-min composition.

Apoptosis repressor with caspase recruitment domain is regulated by MAPK/PI3K and confers drug resistance and survival advantage to AML.

The apoptosis repressor with caspase recruitment domain (ARC) protein is known to suppress both intrinsic and extrinsic apoptosis. We previously reported that ARC expression is a strong, independent adverse prognostic factor in acute myeloid leukemia (AML). Here, we investigated the regulation and role of ARC in AML. ARC expression is upregulated in AML cells co-cultured with bone marrow-derived mesenchymal stromal cells (MSCs) and suppressed by inhibition of MAPK and PI3K signaling. AML patient samples with RAS mutations (N = 64) expressed significantly higher levels of ARC than samples without RAS mutations (N = 371) (P = 0.016). ARC overexpression protected and ARC knockdown sensitized AML cells to cytarabine and to agents that selectively induce intrinsic (ABT-737) or extrinsic (TNF-related apoptosis inducing ligand) apoptosis. NOD-SCID mice harboring ARC-overexpressing KG-1 cells had significantly shorter survival than mice injected with control cells (median 84 vs 111 days) and significantly fewer leukemia cells were present when NOD/SCID IL2Rγ null mice were injected with ARC knockdown as compared to control Molm13 cells (P = 0.005 and 0.03 at 2 and 3 weeks, respectively). Together, these findings demonstrate that MSCs regulate ARC in AML through activation of MAPK and PI3K signaling pathways. ARC confers drug resistance and survival advantage to AML in vitro and in vivo, suggesting ARC as a novel target in AML therapy.

Control of type 2 diabetes after 1 year of laparoscopic adjustable gastric banding in the helping evaluate reduction in obesity (HERO) study.

AIMS: The 5-year, open-label, prospective, observational helping evaluate reduction in obesity (HERO) study (N = 1106) examines efficacy and safety of the LAP-BAND AP(®) laparoscopic adjustable gastric band (LAGB) in obese patients. This interim analysis assessed the control of type 2 diabetes (T2D), 1 year after the implantation of the LAGB. METHODS: Baseline T2D was defined by chart review or use of antidiabetic medications or haemoglobin A1c (HbA1c) ≥ 7.0%. Control of T2D at 1 year was defined as A1c <7.0% (with or without antidiabetic medications). RESULTS: After 1 year, 187 of 273 patients with T2D at baseline had adequate data available to assess T2D status, of which 135 patients (72.2%) achieved target control of T2D compared with 42.8% control rate at baseline. Independent predictors of achieving target control at 1 year included the following: (i) shorter diabetes duration odds ratio (OR) 0.914 [95% confidence interval (CI), 0.839, 0.995, p = 0.038], (ii) not using insulin therapy OR 0.16 (95% CI, 0.06, 0.47, p < 0.001) and (iii) greater mean % weight loss OR 1.176 (95% CI, 1.093, 1.266, p < 0.001). Patients using insulin at baseline were 84% less likely to achieve control of T2D after 1 year; each additional year of diabetes at baseline reduced the likelihood of good control by 9%; and each 1% of weight loss increases the likelihood of good control by 18%. Rates of device-related adverse events and reoperations were low and were not significantly different between patients with and without baseline T2D at 1 year. CONCLUSIONS: Greater % weight loss, not using insulin therapy, and shorter disease duration predicted increased likelihood of target control of T2D, 1 year after implantation of the LAGB.

The impact of a vaccine mandate and the COVID-19 pandemic on influenza vaccination uptake in Western Australian health care students.

Annual influenza vaccination of health care students and workers helps protect themselves and patients from influenza, which has a high disease burden during seasonal peaks in Australia. Health care students are an important cohort whose early attitudes and habits towards influenza vaccination may influence future behaviours. We explored the knowledge, attitudes, and behaviours towards influenza vaccination of health care students in two universities from 2018 to 2020 using convergent mixed methodology. We also assessed the impact of two external events - the introduction of mandatory influenza vaccination for select students in 2019, and the COVID-19 pandemic in 2020. We found a significant increase in self-reported vaccination uptake between 2018 (73.5%) and 2020 (89.6%), with the mandate and COVID-19 pandemic being likely drivers of increased uptake. Vaccine mandates are effective but must be supported by easy accessibility, adequately addressing concerns around effectiveness and safety, and promotion of voluntary acceptance and trust.

Secondary attack rate of pandemic influenza A(H1N1) 2009 in Western Australian households, 29 May-7 August 2009.

Understanding household transmission of the pandemic influenza A(H1N1)2009 virus, including risk factors for transmission, is important for refining public health strategies to reduce the burden of the disease. During the influenza season of 2009 we investigated transmission of the emerging virus in 595 households in which the index case was the first symptomatic case of influenza A(H1N1)2009. Secondary cases were defined as household contacts with influenza-like illness (ILI) or laboratory-confirmed influenza A(H1N1)2009, occurring at least one day after but within seven days following symptom onset in the index case. ILI developed in 231 of the 1,589 household contacts, a secondary attack rate of 14.5% (95% confidence interval (CI): 12.9­16.4). At least one secondary case occurred in 166 of the 595 households (a household transmission rate of 27.9%; 95% CI: 24.5­31.6).Of these, 127 (76.5%) households reported one secondary case and 39 (23.5%) households reported two or more secondary cases. Secondary attack rates were highest in children younger than five years (p=0.001), and young children were also more efficient transmitters (p=0.01). Individual risk was not associated with household size. Prophylactic antiviral therapy was associated with reduced transmission (p=0.03). The secondary attack rate of ILI in households with a confirmed pandemic influenza A(H1N1)2009 index case was comparable to that described previously for seasonal influenza.

Association between 2009 seasonal influenza vaccine and influenza-like illness during the 2009 pandemic: preliminary results of a large household transmission study in Western Australia.

We conducted a prospective household transmission study to examine whether receipt of 2009 trivalent influenza vaccine (TIV) was associated with increased risk of influenza-like illness (ILI) among contacts of confirmed pandemic influenza A(H1N1) 2009 patients. In the week following onset of pandemic illness in a household member, 46 (15%) of 304 TIV-vaccinated contacts, and 174 (15%) of 1,162 unvaccinated contacts developed ILI (p=0.95). Receipt of 2009 TIV had no effect on one's risk of pandemic illness.

Cystic fibrosis transmembrane conductance regulator-associated ATP release is controlled by a chloride sensor.

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel that is defective in cystic fibrosis, and has also been closely associated with ATP permeability in cells. Using a Xenopus oocyte cRNA expression system, we have evaluated the molecular mechanisms that control CFTR-modulated ATP release. CFTR-modulated ATP release was dependent on both cAMP activation and a gradient change in the extracellular chloride concentration. Activation of ATP release occurred within a narrow concentration range of external Cl- that was similar to that reported in airway surface fluid. Mutagenesis of CFTR demonstrated that Cl- conductance and ATP release regulatory properties could be dissociated to different regions of the CFTR protein. Despite the lack of a need for Cl- conductance through CFTR to modulate ATP release, alterations in channel pore residues R347 and R334 caused changes in the relative ability of different halides to activate ATP efflux (wtCFTR, Cl >> Br; R347P, Cl >> Br; R347E, Br >> Cl; R334W, Cl = Br). We hypothesize that residues R347 and R334 may contribute a Cl- binding site within the CFTR channel pore that is necessary for activation of ATP efflux in response to increases of extracellular Cl-. In summary, these findings suggest a novel chloride sensor mechanism by which CFTR is capable of responding to changes in the extracellular chloride concentration by modulating the activity of an unidentified ATP efflux pathway. This pathway may play an important role in maintaining fluid and electrolyte balance in the airway through purinergic regulation of epithelial cells. Insight into these molecular mechanisms enhances our understanding of pathogenesis in the cystic fibrosis lung.

Treat-early and treat-mild: role of fast vs. slow escalation of headaches.

This prospective, multi-center, observational study aimed to examine patients' early treatment decision process. Specifically, we assessed if the association between mild headache pain at treatment initiation and early treatment differed by the speed of headache escalation. Patients (n = 168) were instructed to collect information on their headache experience during the study period via an electronic diary over 30 consecutive days after enrollment. At the time of treatment, patients who treated early were 2.3 times as likely to experience mild headache pain as those who treated late. Controlling for the effect of escalation of headache, patients who treated early were three times as likely to report mild headache pain at dosing as those who treated late. The interaction between fast escalation of headache and mild pain was not statistically significant. Early treatment is associated with mild pain, regardless of the speed of headache escalation.

Incisor root resorption due to ectopic maxillary canines: a long-term radiographic follow-up.

OBJECTIVE: To document the long-term fate of maxillary incisors with resorbed roots after correction of the associated ectopic canines. MATERIALS AND METHODS: The subjects were recruited from 107 children and adolescents age 9-15 years (mean 12.5 years) at initial registration, with 156 ectopically positioned maxillary canines. The children were referred to the specialist orthodontic clinic for consultation because of the risk of incisor root resorption. Of 51 patients contacted, 16 failed to attend. Eight of the remaining 35 were excluded because their lateral incisors had been extracted, leaving 27 subjects for follow-up registration. At initial consultation, all subjects had undergone radiographic examination, including computed tomography (CT) scans. At the follow-up consultation, the radiographic examination was limited to intraoral films. RESULTS: No resorbed incisor was lost during the 2- to 10-year follow-up period. The resorptive lesions had undergone repair in 13 teeth, remained unchanged in 12 teeth and progressed in 7 teeth. In the 13 teeth exhibiting signs of repair, no resorption was detectable in 11 teeth and minor resorption was detected in 2 lateral incisors. At the initial registration, severe or moderate resorption had been diagnosed in 12 lateral and 5 central incisors, compared with 11 lateral and 6 central incisors at follow-up. In 10 subjects initially diagnosed with resorption of 13 incisors, the lesions were no longer discernible on intraoral radiographs at follow-up. CONCLUSIONS: Even in cases of severe resorption, the incisor roots show good long-term healing. Incisors with root resorption can be used in an orthodontic appliance system.

Tumor inhibitory effects of intravesical Ganoderma lucidum instillation in the syngeneic orthotopic MB49/C57 bladder cancer mice model.

ETHNOPHARMACOLOGICAL RELEVANCE: Ganoderma lucidum (GL) has been traditionally used in oriental medicine as superior health tonic, and there are numerous scientific evidences of its antitumorigenic activities. AIM OF THE STUDY: To evaluate the intravesical chemopreventive effects of ethanol extract of GL (GLe) on bladder cancer. MATERIALS AND METHODS: Intravesical therapy is defined as the direct instillation of a liquid drug into bladder through a catheter. Bacille Calmette-Guerin(BCG) solution is applied intravesically as a conventional immunotherapy for preventing recurrence of bladder cancer. By adopting the MB49/C57 bladder cancer mice model, an overall 60 MB49-implanted mice were randomized into 3 groups and treated according to 3 treatment arms, including GLe, BCG and PBS. Additionally, wild-type mice without MB49 cell inoculation and treated with PBS were used as the negative control group. Testing agents were instilled intravesically for 2 h and repeated after one week for evaluating the effects on preventing the tumor formation and growth. The treated-mice were closely monitored for major adverse effects. RESULTS: GLe demonstrated more potent cytotoxic effects than BCG on MB49 cells, although both in dose-dependent manner. In the MB49-implanted mice, 80 µg/ml GLe was shown to delay the tumor formation by one week, whereas the averaged tumor volume measured at endpoint was 3.6-fold and 4.6-fold smaller than that of the BCG or PBS, respectively. However, no significant effects were observed on body weight and hematuria. CONCLUSION: Current findings in mice suggested intravesical GLe therapy as an effective and safe chemopreventive strategy for inhibiting bladder tumor formation.

Long-term impact of childhood hepatitis B vaccination programs on prevalence among Aboriginal and non-Aboriginal women giving birth in Western Australia.

BACKGROUND/AIMS: To evaluate the long-term effect of infant and childhood hepatitis B (HBV) vaccination programs among birthing women in Western Australia. METHODS: A cohort of Western Australian women born from 1974 to 1995 was created using Birth Registrations and Electoral Roll records. They were linked to a perinatal register and notifiable diseases register to identify women having respectively their first births between 2000 and 2012 and diagnoses of HBV infections. HBV prevalence was estimated in Aboriginal and non-Aboriginal women, and according to maternal birth year cohorts. RESULTS: Of 66,073 women, 155 (0.23%) had a linked non-acute HBV notification. HBV prevalence was five times higher in Aboriginal women compared to their non-Aboriginal counterparts (0.92%, 95%CI 0.65-1.18 versus 0.18%, 0.15-0.21). Among Aboriginal women, after adjusting for year of giving birth and region of residence, those born in the targeted infant and school-based vaccination era (maternal year of birth 1988-1995) had an 89% lower risk (adjusted odds ratio [aOR] 0.11, 0.04-0.33) of HBV than those born in the pre-vaccination era (1974-1981). Prevalence also differed between Aboriginal women residing in rural/remote areas compared to those in major cities (aOR 3.06, 1.36-6.88). Among non-Aboriginal women, no significant difference in HBV prevalence was observed by maternal birth cohort (p = 0.20) nor by residence (p = 0.23), but there were significant differences by ethnicity with a 36-fold higher prevalence (aOR 36.08, 22.66-57.46) in non-Caucasian versus Caucasian women. CONCLUSIONS: A significant decline in HBV prevalence in Aboriginal birthing mothers was observed following the introduction of HBV vaccination programs in Western Australia. There were also considerable disparities in prevalence between women by area of residence and ethnicity. Our findings reflect those observed in women in other Australian jurisdictions. Continued surveillance of HBV prevalence in birthing mothers will provide ongoing estimates of HBV vaccination program impact across Australia and the populations most at risk of chronic HBV.

Combined inhibition of ß-catenin and Bcr-Abl synergistically targets tyrosine kinase inhibitor-resistant blast crisis chronic myeloid leukemia blasts and progenitors in vitro and in vivo.

Tyrosine kinase inhibitor (TKI) resistance and progression to blast crisis (BC), both related to persistent ß-catenin activation, remain formidable challenges for chronic myeloid leukemia (CML). We observed overexpression of ß-catenin in BC-CML stem/progenitor cells, particularly in granulocyte-macrophage progenitors, and highest among a novel CD34+CD38+CD123hiTim-3hi subset as determined by CyTOF analysis. Co-culture with mesenchymal stromal cells (MSCs) induced the expression of ß-catenin and its target CD44 in CML cells. A novel Wnt/ß-catenin signaling modulator, C82, and nilotinib synergistically killed KBM5T315I and TKI-resistant primary BC-CML cells with or without BCR-ABL kinase mutations even under leukemia/MSC co-culture conditions. Silencing of ß-catenin by short interfering RNA restored sensitivity of primary BCR-ABLT315I/E255V BC-CML cells to nilotinib. Combining the C82 pro-drug, PRI-724, with nilotinib significantly prolonged the survival of NOD/SCID/IL2Rγ null mice injected with primary BCR-ABLT315I/E255V BC-CML cells. The combined treatment selectively targeted CML progenitors and inhibited CD44, c-Myc, survivin, p-CRKL and p-STAT5 expression. In addition, pretreating primary BC-CML cells with C82, or the combination, but not with nilotinib alone, significantly impaired their engraftment potential in NOD/SCID/IL2Rγ-null-3/GM/SF mice and significantly prolonged survival. Our data suggest potential benefit of concomitant ß-catenin and Bcr-Abl inhibition to prevent or overcome Bcr-Abl kinase-dependent or -independent TKI resistance in BC-CML.

The benefits of newborn screening for cystic fibrosis: The Canadian experience.

BACKGROUND: The impact of newborn screening (NBS) for cystic fibrosis (CF) on early indicators of long-term health was evaluated in the context of government-sponsored healthcare and access to current therapies. METHODS: Using data from the Canadian CF Registry between 2008 and 2013, we compared the rates of respiratory infections and markers of nutritional status in those diagnosed through NBS to those who were diagnosed clinically within the same time period using Mann-Whitney and Fischer's exact test as appropriate. RESULTS: The study included 303 subjects, 201 in the NBS group and 102 in the non-NBS group. NBS patients were diagnosed earlier and had their first clinic visit at a younger age. Pancreatic insufficiency was less common in NBS patients. The incidence of Pseudomonas aeruginosa and Staphylococcus aureus were lower in NBS patients. After adjusting for age at clinic visit, gender, pancreatic status, and Pseudomonas aeruginosa infection status, mean z-scores for weight-for-age and height-for-age were higher in NBS patients, with no differences in BMI-for-age. CONCLUSIONS: NBS programs for CF lead to improved long-term health outcomes for the CF population.

Single-channel kinetics, inactivation, and spatial distribution of inositol trisphosphate (IP3) receptors in Xenopus oocyte nucleus.

Single-channel properties of the Xenopus inositol trisphosphate receptor (IP3R) ion channel were examined by patch clamp electrophysiology of the outer nuclear membrane of isolated oocyte nuclei. With 140 mM K+ as the charge carrier (cytoplasmic [IP3] = 10 microM, free [Ca2+] = 200 nM), the IP3R exhibited four and possibly five conductance states. The conductance of the most-frequently observed state M was 113 pS around 0 mV and approximately 300 pS at 60 mV. The channel was frequently observed with high open probability (mean P(o) = 0.4 at 20 mV). Dwell time distribution analysis revealed at least two kinetic states of M with time constants tau < 5 ms and approximately 20 ms; and at least three closed states with tau approximately 1 ms, approximately 10 ms, and >1 s. Higher cytoplasmic potential increased the relative frequency and tau of the longest closed state. A novel "flicker" kinetic mode was observed, in which the channel alternated rapidly between two new conductance states: F1 and F2. The relative occupation probability of the flicker states exhibited voltage dependence described by a Boltzmann distribution corresponding to 1.33 electron charges moving across the entire electric field during F1 to F2 transitions. Channel run-down or inactivation (tau approximately 30 s) was consistently observed in the continuous presence of IP3 and the absence of change in [Ca2+]. Some (approximately 10%) channel disappearances could be reversed by an increase in voltage before irreversible inactivation. A model for voltage-dependent channel gating is proposed in which one mechanism controls channel opening in both the normal and flicker modes, whereas a separate independent mechanism generates flicker activity and voltage-reversible inactivation. Mapping of functional channels indicates that the IP3R tends to aggregate into microscopic (<1 microm) as well as macroscopic (approximately 10 microm) clusters. Ca2+-independent inactivation of IP3R and channel clustering may contribute to complex [Ca2+] signals in cells.

Regulation by Ca2+ and inositol 1,4,5-trisphosphate (InsP3) of single recombinant type 3 InsP3 receptor channels. Ca2+ activation uniquely distinguishes types 1 and 3 insp3 receptors.

The inositol 1,4,5-trisphosphate (InsP(3)) receptor (InsP3R) is an endoplasmic reticulum-localized Ca2+ -release channel that controls complex cytoplasmic Ca(2+) signaling in many cell types. At least three InsP3Rs encoded by different genes have been identified in mammalian cells, with different primary sequences, subcellular locations, variable ratios of expression, and heteromultimer formation. To examine regulation of channel gating of the type 3 isoform, recombinant rat type 3 InsP3R (r-InsP3R-3) was expressed in Xenopus oocytes, and single-channel recordings were obtained by patch-clamp electrophysiology of the outer nuclear membrane. Gating of the r-InsP3R-3 exhibited a biphasic dependence on cytoplasmic free Ca2+ concentration ([Ca2+]i). In the presence of 0.5 mM cytoplasmic free ATP, r-InsP3R-3 gating was inhibited by high [Ca2+]i with features similar to those of the endogenous Xenopus type 1 Ins3R (X-InsP3R-1). Ca2+ inhibition of channel gating had an inhibitory Hill coefficient of approximately 3 and half-maximal inhibiting [Ca2+]i (Kinh) = 39 microM under saturating (10 microM) cytoplasmic InsP3 concentrations ([InsP3]). At [InsP3] < 100 nM, the r-InsP3R-3 became more sensitive to Ca2+ inhibition, with the InsP(3) concentration dependence of Kinh described by a half-maximal [InsP3] of 55 nM and a Hill coefficient of approximately 4. InsP(3) activated the type 3 channel by tuning the efficacy of Ca2+ to inhibit it, by a mechanism similar to that observed for the type 1 isoform. In contrast, the r-InsP3R-3 channel was uniquely distinguished from the X-InsP3R-1 channel by its enhanced Ca2+ sensitivity of activation (half-maximal activating [Ca2+]i of 77 nM instead of 190 nM) and lack of cooperativity between Ca2+ activation sites (activating Hill coefficient of 1 instead of 2). These differences endow the InsP3R-3 with high gain InsP3-induced Ca2+ release and low gain Ca2+ -induced Ca2+ release properties complementary to those of InsP3R-1. Thus, distinct Ca2+ signals may be conferred by complementary Ca2+ activation properties of different InsP3R isoforms.